The general objectives of this investigation are concerned with carrying out an in-depth study of the chemistry and biotransformation of the anticancer drug 4'-(9-acridinylamino)-methanesulfon-m-anisidide (NSC 249992, m-AMSA) and selected related compounds in experimental animals. In vitro studies employing the hepatic microsomal drug metabolism system has provided evidence that m-AMSA is oxidized to a quinoidal intermediate which reacts rapidly with glutathione to form a conjugate that is the principal rat biliary metabolite. The quinoidal intermediate reacts readily with the nucleophilic groups of cellular macromolecules which may possibly account for the cytotoxicity of m-AMSA.